Rubber composition and tire

ABSTRACT

The present invention relates to a rubber composition including (A) at least one rubber component selected from the group consisting of a synthetic rubber and a natural rubber; (B) a polymer of farnesene; and (C) carbon black having an average particle size of from 5 to 100 nm, a content of the carbon black (C) in the rubber composition being from 20 to 100 parts by mass on the basis of 100 parts by mass of the rubber component (A).

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a 35 U.S.C. §371 national stage patentapplication of International patent application PCT/JP2012/074168, filedon Sep. 21, 2012, published as WO/2013/047347 on Apr. 4, 2013, the textof which is incorporated by reference, and claims the benefit of thefiling date of Japanese application nos. 2011-218119, filed on Sep. 30,2011, and 2012-039412, filed on Feb. 24, 2012, the text of each of whichis also incorporated by reference.

TECHNICAL FIELD

The present invention relates to a rubber composition containing arubber component, a polymer of farnesene and carbon black, and a tireusing the rubber composition.

BACKGROUND ART

Hitherto, in the application field of tires for which a wear resistanceand a mechanical strength are required, there have been extensively usedrubber compositions that are enhanced in mechanical strength byincorporating a reinforcing agent such as carbon black in a rubbercomponent such as a natural rubber and a styrene-butadiene rubber.

It is known that the carbon black exhibits its reinforcing effect byphysically or chemically adsorbing the aforementioned rubber componentonto a surface of respective particles of the carbon black.

However, when the particle size of the carbon black used in the rubbercomposition is as large as from about 100 to about 200 nm, it isgenerally difficult to attain a sufficient interaction between thecarbon black and the rubber component, so that the resulting rubbercomposition tends to be hardly improved in mechanical strength to asufficient extent.

In addition, tires produced from such a rubber composition tend toexhibit a low hardness and therefore tend to be insufficient in steeringstability.

On the other hand, when the carbon black used in the rubber compositionhas an average particle size as small as from about 5 to about 100 nmand therefore a large specific surface area, the resulting rubbercomposition can be improved in properties such as mechanical strengthand wear resistance owing to a large interaction between the carbonblack and the rubber component.

In addition, tires produced from such a rubber composition can beimproved in steering stability owing to an increased hardness thereof.

However, in the case where the carbon black having such a small averageparticle size is used in the rubber composition, it is known that theresulting rubber composition tends to be deteriorated in dispersibilityof the carbon black therein owing to a high cohesive force between thecarbon black particles.

The deteriorated dispersibility of the carbon black in the rubbercomposition tends to induce a prolonged kneading step and thereforetends to give an adverse influence on productivity of the rubbercomposition.

Also, the deteriorated dispersibility of the carbon black tends to causegeneration of heat in the rubber composition, so that tires producedtherefrom tend to be deteriorated in rolling resistance performance andmay frequently fail to satisfy the requirements for low rollingresistance tires (so-called low-fuel consumption tires).

Further, in the case where the carbon black used in the rubbercomposition has a small average particle size, there tends to occur sucha problem that the resulting rubber composition exhibits a highviscosity and therefore is deteriorated in processability.

Thus, the mechanical strength and hardness of the rubber composition fortires are properties having a contradictory relation with the rollingresistance performance and processability thereof, and it is thereforeconsidered that the rubber composition is hardly improved in both of theproperties in a well-balanced manner.

In Patent Document 1, as a rubber composition that can be improved inthe aforementioned properties in a well-balanced manner, there isdescribed the rubber composition for tires which includes a rubbercomponent containing an isoprene-based rubber and a styrene-butadienerubber, carbon black and a liquid resin having a softening point of from−20 to 20° C. at a specific compounding ratio.

Also, Patent Document 2 describes the tire including a rubber componentcontaining a diene-based rubber constituted of a modifiedstyrene-butadiene copolymer and a modified conjugated diene-basedpolymer, and a filler such as carbon black at a specific compoundingratio.

However, any of the tires described in these Patent Documents fail tosatisfy the mechanical strength and hardness as well as the rollingresistance performance and processability with a sufficiently highlevel, and therefore there is still a strong demand for tires that arefurther improved in these properties.

Meanwhile, Patent Documents 3 and 4 describe a polymer of β-farnesene,but fail to have a sufficient study on practical applications thereof.

CITATION LIST Patent Literature

Patent Document 1: JP 2011-195804A

Patent Document 2: JP 2010-209256A

Patent Document 3: WO 2010/027463A

Patent Document 4: WO 2010/027464A

SUMMARY OF INVENTION Technical Problem

The present invention has been made in view of the above conventionalproblems. The present invention provides a rubber composition thatexhibits not only a good processability upon compounding, molding orcuring, but also an excellent rolling resistance performance owing to animproved dispersibility of carbon black therein, and further hardlysuffers from deterioration in mechanical strength and hardness, and atire obtained using the rubber composition.

Solution to Problem

As a result of extensive and intensive researches, the present inventorshave found that when using a conjugated diene-based polymer having aspecific structure, the resulting rubber composition can be improved inprocessability, can exhibit a low rolling resistance owing to animproved dispersibility of carbon black therein, and further hardlysuffers from deterioration in mechanical strength and hardness. Thepresent invention has been accomplished on the basis of the abovefinding.

That is, the present invention relates to the following aspects.

[1] A rubber composition including (A) at least one rubber componentselected from the group consisting of a synthetic rubber and a naturalrubber; (B) a polymer of farnesene; and (C) carbon black having anaverage particle size of from 5 to 100 nm, a content of the carbon black(C) in the rubber composition being from 20 to 100 parts by mass on thebasis of 100 parts by mass of the rubber component (A), and[2] A tire at least partially including the above rubber composition.

Advantageous Effects of Invention

According to the present invention, there are provided a rubbercomposition that has not only a good processability upon compounding,molding or curing, but also an excellent rolling resistance performanceowing to an improved dispersibility of carbon black therein, and furtherhardly suffers from deterioration in mechanical strength and hardness,and a tire obtained using the rubber composition.

DESCRIPTION OF EMBODIMENTS

[Rubber Composition]

The rubber composition of the present invention includes (A) at leastone rubber component selected from the group consisting of a syntheticrubber and a natural rubber; (B) a polymer of farnesene; and (C) carbonblack having an average particle size of from 5 to 100 nm, in which acontent of the carbon black (C) in the rubber composition is from 20 to100 parts by mass on the basis of 100 parts by mass of the rubbercomponent (A).

<Rubber Component (A)>

(1) Synthetic Rubber

Examples of the synthetic rubber used herein include a styrene-butadienerubber (hereinafter occasionally referred to merely as “SBR”), anisoprene rubber, a butadiene rubber, a butyl rubber, a halogenated butylrubber, an ethylene propylene diene rubber, a butadiene acrylonitrilecopolymer rubber and a chloroprene rubber. Among these syntheticrubbers, preferred are SBR, an isoprene rubber and a butadiene rubber.These synthetic rubbers may be used alone or in combination of any twoor more thereof.

(SBR (A-1))

As SBR (A-1), there may be used those generally used in the applicationsof tires. More specifically, the SBR (A-1) preferably has a styrenecontent of from 0.1 to 70% by mass and more preferably from 5 to 50% bymass. Also, the SBR (A-1) preferably has a vinyl content of from 0.1 to60% by mass and more preferably from 0.1 to 55% by mass.

The weight-average molecular weight (Mw) of the SBR (A-1) is preferablyfrom 100,000 to 2,500,000, more preferably from 150,000 to 2,000,000 andstill more preferably from 200,000 to 1,500,000. When the weight-averagemolecular weight of the SBR (A-1) falls within the above-specifiedrange, the resulting rubber composition can be enhanced in bothprocessability and mechanical strength. Meanwhile, in the presentspecification, the weight-average molecular weight is the value measuredby the method described below in Examples.

The glass transition temperature (Tg) of the SBR used in the presentinvention as measured by differential thermal analysis is preferablyfrom −95° C. to 0° C. and more preferably from −95° C. to −5° C. Whenadjusting Tg of the SBR to the above-specified range, it is possible tosuppress increase in viscosity of the SBR and enhance a handlingproperty thereof.

<<Method for Producing SBR (A-1)>>

The SBR (A-1) usable in the present invention may be produced bycopolymerizing styrene and butadiene. The production method of the SBRis not particularly limited, and the SBR may be produced by any of anemulsion polymerization method, a solution polymerization method, avapor phase polymerization method and a bulk polymerization method.Among these polymerization methods, especially preferred are an emulsionpolymerization method and a solution polymerization method.

(i) Emulsion-Polymerized Styrene-Butadiene Rubber (E-SBR)

E-SBR may be produced by an ordinary emulsion polymerization method. Forexample, a predetermined amount of a styrene monomer and a predeterminedamount of a butadiene monomer are emulsified and dispersed in thepresence of an emulsifying agent and then subjected to emulsionpolymerization using a radical polymerization initiator.

As the emulsifying agent, there may be used a long-chain fatty acid salthaving 10 or more carbon atoms or a rosinic acid salt. Specific examplesof the emulsifying agent include potassium salts and sodium salts offatty acids such as capric acid, lauric acid, myristic acid, palmiticacid, oleic acid and stearic acid.

As a dispersant for the above emulsion polymerization, there may beusually used water. The dispersant may also contain a waster-solubleorganic solvent such as methanol and ethanol unless the use of such anorganic solvent gives any adverse influence on stability of thepolymerization.

Examples of the radical polymerization initiator include persulfatessuch as ammonium persulfate and potassium persulfate, organic peroxidesand hydrogen peroxide.

In order to suitably adjust a molecular weight of the obtained E-SBR,there may be used a chain transfer agent. Examples of the chain transferagent include mercaptans such as t-dodecyl mercaptan and n-dodecylmercaptan; and carbon tetrachloride, thioglycolic acid, diterpene,terpinolene, γ-terpinene and an α-methyl styrene dimer.

The temperature used upon the emulsion polymerization may beappropriately determined according to the kind of radical polymerizationinitiator used therein, and is usually preferably from 0 to 100° C. andmore preferably from 0 to 60° C. The polymerization method may be eithera continuous polymerization method or a batch polymerization method. Thepolymerization reaction may be stopped by adding a terminating agent tothe reaction system.

Examples of the terminating agent include amine compounds such asisopropyl hydroxylamine, diethyl hydroxylamine and hydroxylamine;quinone-based compounds such as hydroquinone and benzoquinone; andsodium nitrite.

After terminating the polymerization reaction, an antioxidant may beadded, if required. Further, after stopping the polymerization reaction,unreacted monomers may be removed from the resulting latex, if required.Thereafter, the obtained polymer is coagulated by adding a salt such assodium chloride, calcium chloride and potassium chloride as a coagulantthereto and, if required, while adjusting a pH value of the coagulationsystem by adding an acid such as nitric acid and sulfuric acid thereto,and then the dispersing solvent is separated from the reaction solutionto recover the polymer as a crumb. The thus recovered crumb is washedwith water and dehydrated, and then dried using a band dryer or the liketo obtain E-SBR.

Meanwhile, upon coagulating the polymer, the latex may be previouslymixed with an extender oil in the form of an emulsified dispersion torecover the polymer in the form of an oil-extended rubber.

(ii) Solution-Polymerized Styrene-Butadiene Rubber (S-SBR)

S-SBR may be produced by an ordinary solution polymerization method. Forexample, styrene and butadiene are polymerized in a solvent using ananion-polymerizable active metal, if required, in the presence of apolar compound.

Examples of the solvent include aliphatic hydrocarbons such as n-butane,n-pentane, isopentane, n-hexane, n-heptane and isooctane; alicyclichydrocarbons such as cyclopentane, cyclohexane and methyl cyclopentane;and aromatic hydrocarbons such as benzene and toluene. These solventsmay be usually used in such a range that a monomer is dissolved thereinat a concentration of from 1 to 50% by mass.

Examples of the anion-polymerizable active metal include alkali metalssuch as lithium, sodium and potassium; alkali earth metals such asberyllium, magnesium, calcium, strontium and barium; andlanthanoid-based rare earth metals such as lanthanum and neodymium.Among these active metals, preferred are alkali metals and alkali earthmetals, and more preferred are alkali metals. The alkali metals are morepreferably used in the form of an organic alkali metal compound.

Specific examples of the organic alkali metal compound include organicmonolithium compounds such as n-butyl lithium, sec-butyl lithium,t-butyl lithium, hexyl lithium, phenyl lithium and stilbene lithium;polyfunctional organic lithium compounds such as dilithiomethane,1,4-dilithiobutane, 1,4-dilithio-2-ethyl cyclohexane and1,3,5-trilithiobenzene; and sodium naphthalene and potassiumnaphthalene. Among these organic alkali metal compounds, preferred areorganic lithium compounds, and more preferred are organic monolithiumcompounds. The amount of the organic alkali metal compound used may beappropriately determined according to a molecular weight of S-SBR asrequired.

The organic alkali metal compound may be used in the form of an organicalkali metal amide by allowing a secondary amine such as dibutyl amine,dihexyl amine and dibenzyl amine to react therewith.

The polar compound used in the solution polymerization is notparticularly limited as long as the compound do not cause deactivationof the reaction and can be ordinarily used for controlling amicrostructure of butadiene moieties and distribution of styrene in acopolymer chain thereof. Examples of the polar compound include ethercompounds such as dibutyl ether, tetrahydrofuran and ethylene glycoldiethyl ether; tertiary amines such as tetramethyl ethylenediamine andtrimethylamine; and alkali metal alkoxides and phosphine compounds.

The temperature used in the above polymerization reaction is usuallyfrom −80 to 150° C., preferably from 0 to 100° C. and more preferablyfrom 30 to 90° C. The polymerization method may be either a batch methodor a continuous method. Also, in order to improve a randomcopolymerizability between styrene and butadiene, the styrene andbutadiene are preferably supplied to a reaction solution in a continuousor intermittent manner such that a compositional ratio between thestyrene and butadiene in the polymerization system falls within aspecific range.

The polymerization reaction may be stopped by adding an alcohol such asmethanol and isopropanol as a terminating agent to the reaction system.In addition, before adding the terminating agent, there may be added acoupling agent such as tin tetrachloride, tetrachlorosilane,tetramethoxysilane, tetraglycidyl-1,3-bisaminomethyl cyclohexane and2,4-tolylene diisocyanate which are capable of reacting with an activeend of the polymer chain, and a chain end-modifying agent such as4,4′-bis(diethylamino)benzophenone and N-vinyl pyrrolidone. Thepolymerization reaction solution obtained after terminating thepolymerization reaction may be directly subjected to drying or steamstripping to remove the solvent therefrom, thereby recovering the S-SBRas aimed. Meanwhile, before removing the solvent, the polymerizationreaction solution may be previously mixed with an extender oil torecover the S-SBR in the form of an oil-extended rubber.

[Modified Styrene-Butadiene Rubber (Modified SBR)]

In the present invention, there may also be used a modified SBR producedby introducing a functional group into SBR. Examples of the functionalgroup to be introduced include an amino group, an alkoxysilyl group, ahydroxyl group, an epoxy group and a carboxyl group.

In the modified SBR, the site of the polymer into which the functionalgroup is introduced may be either a chain end or a side chain of thepolymer.

(Isoprene Rubber (A-2))

The isoprene rubber may be a commercially available isoprene rubberwhich may be obtained by the polymerization using a Ziegler-basedcatalyst such as titanium tetrahalide-trialkyl aluminum-based catalysts,diethyl aluminum chloride-cobalt-based catalysts, trialkylaluminum-boron trifluoride-nickel-based catalysts and diethyl aluminumchloride-nickel-based catalysts; a lanthanoid-based rare earth metalcatalyst such as triethyl aluminum-organic acid neodymium salt-Lewisacid-based catalysts; and an organic alkali metal compound as usedsimilarly for production of the S-SBR. Among these isoprene rubbers,preferred are isoprene rubbers obtained by the polymerization using theZiegler-based catalyst because of a high cis isomer content thereof. Inaddition, there may also be used those isoprene rubbers having anultrahigh cis isomer content which are produced using thelanthanoid-based rare earth metal catalyst.

The isoprene rubber has a vinyl content of 50% by mass or less,preferably 40% by mass or less, and more preferably 30% by mass or less.When the vinyl content of the isoprene rubber is more than 50% by mass,the resulting rubber composition tends to be deteriorated in rollingresistance performance. The lower limit of the vinyl content of theisoprene rubber is not particularly limited. The glass transitiontemperature of the isoprene rubber may vary depending upon the vinylcontent thereof, and is preferably −20° C. or lower and more preferably−30° C. or lower.

The weight-average molecular weight of the isoprene rubber is preferablyfrom 90,000 to 2,000,000 and more preferably from 150,000 to 1,500,000.When the weight-average molecular weight of the isoprene rubber fallswithin the above-specified range, the resulting rubber composition canexhibit a good processability and a good mechanical strength.

The isoprene rubber may partially have a branched structure or maypartially contain a polar functional group by using a polyfunctionaltype modifying agent, for example, a modifying agent such as tintetrachloride, silicon tetrachloride, an alkoxysilane containing anepoxy group in a molecule thereof, and an amino group-containingalkoxysilane.

(Butadiene Rubber (A-3))

The butadiene rubber may be a commercially available butadiene rubberwhich may be obtained by the polymerization using a Ziegler-basedcatalyst such as titanium tetrahalide-trialkyl aluminum-based catalysts,diethyl aluminum chloride-cobalt-based catalysts, trialkylaluminum-boron trifluoride-nickel-based catalysts and diethyl aluminumchloride-nickel-based catalysts; a lanthanoid-based rare earth metalcatalyst such as triethyl aluminum-organic acid neodymium salt-Lewisacid-based catalysts; and an organic alkali metal compound as usedsimilarly for production of the S-SBR. Among these butadiene rubbers,preferred are butadiene rubbers obtained by the polymerization using theZiegler-based catalyst because of a high cis isomer content thereof. Inaddition, there may also be used those butadiene rubbers having anultrahigh cis isomer content which are produced using thelanthanoid-based rare earth metal catalyst.

The butadiene rubber has a vinyl content of 50% by mass or less,preferably 40% by mass or less, and more preferably 30% by mass or less.When the vinyl content of the butadiene rubber is more than 50% by mass,the resulting rubber composition tends to be deteriorated in rollingresistance performance. The lower limit of the vinyl content of thebutadiene rubber is not particularly limited. The glass transitiontemperature of the butadiene rubber may vary depending upon the vinylcontent thereof, and is preferably −40° C. or lower and more preferably−50° C. or lower.

The weight-average molecular weight of the butadiene rubber ispreferably from 90,000 to 2,000,000 and more preferably from 150,000 to1,500,000. When the weight-average molecular weight of the butadienerubber falls within the above-specified range, the resulting rubbercomposition can exhibit a good processability and a good mechanicalstrength.

The butadiene rubber may partially have a branched structure or maypartially contain a polar functional group by using a polyfunctionaltype modifying agent, for example, a modifying agent such as tintetrachloride, silicon tetrachloride, an alkoxysilane containing anepoxy group in a molecule thereof, and an amino group-containingalkoxysilane.

As the rubber component other than the SBR, the isoprene rubber and thebutadiene rubber, there may be used one or more rubbers selected fromthe group consisting of a butyl rubber, a halogenated butyl rubber, anethylene-propylene rubber, a butadiene-acrylonitrile copolymer rubberand a chloroprene rubber. The method of producing these rubbers is notparticularly limited, and any suitable commercially available rubbersmay also be used in the present invention.

In the present invention, when using the SBR, the isoprene rubber, thebutadiene rubber and the other synthetic rubber in combination with thebelow-mentioned polymer (B) of farnesene, it is possible to improve aprocessability of the resulting rubber composition, a dispersibility ofcarbon black therein and a rolling resistance performance thereof.

When using a mixture of two or more kinds of synthetic rubbers, thecombination of the synthetic rubbers may be optionally selected unlessthe effects of the present invention are adversely influenced. Also,various properties of the resulting rubber composition such as a rollingresistance performance and a wear resistance may be appropriatelycontrolled by selecting a suitable combination of the synthetic rubbers.

(2) Natural Rubber

Examples of the natural rubber include TSR such as SMR, SIR and STR;natural rubbers ordinarily used in tire industries, such as RSS;high-purity natural rubbers; and modified natural rubbers such asepoxidized natural rubbers, hydroxylated natural rubbers, hydrogenatednatural rubbers and grafted natural rubbers. Among these naturalrubbers, SMR20, STR20 and RSS#3 are preferred from the viewpoints of aless variation in quality and a good availability. These natural rubbersmay be used alone or in combination of any two or more thereof.

The rubber component (A) includes at least one rubber selected from thegroup consisting of a synthetic rubber and a natural rubber. When usingboth of the synthetic rubber and the natural rubber, the compoundingratio between the synthetic rubber and the natural rubber may beoptionally determined.

<Polymer (B) of Farnesene>

The rubber composition of the present invention contains a polymer (B)of farnesene (hereinafter referred to merely as the “polymer (B)”). Thepolymer (B) may be produced, for example, by polymerizing β-farnesenerepresented by the following formula (I) by the below-mentioned method.

The polymer of farnesene used in the present invention may be either apolymer of x-farnesene or a polymer of β-farnesene represented by thefollowing formula (I). From the viewpoint of easiness of production ofthe polymer, preferred is the polymer of β-farnesene.

Meanwhile, in the present specification, the polymer of farnesene meansa polymer containing a constitutional unit derived from farnesene in anamount of preferably 90% by mass or more, more preferably 95% by mass ormore, still more preferably 98% by mass or more, further still morepreferably 99% by mass or more, and most preferably 100% by mass. Thepolymer of farnesene may also contain a constitutional unit derived fromthe other monomers such as butadiene and isoprene.

The weight-average molecular weight of the polymer (B) is preferably25,000 or more, more preferably 30,000 or more, still more preferably35,000 or more and further still more preferably 40,000 or more, andalso is preferably 500,000 or less, more preferably 450,000 or less,still more preferably 400,000 or less and further still more preferably300,000 or less. More specifically, the weight-average molecular weightof the polymer (B) is preferably from 25,000 to 500,000, more preferablyfrom 30,000 to 450,000, still more preferably from 35,000 to 400,000,and further still more preferably from 40,000 to 300,000.

When the weight-average molecular weight of the polymer (B) falls withinthe above-specified range, the resulting rubber composition according tothe present invention has a good processability, and further can beimproved in dispersibility of the carbon black (C) therein and thereforecan exhibit a good rolling resistance performance. Meanwhile, theweight-average molecular weight of the polymer (B) used in the presentspecification is the value measured by the below-mentioned method. Inthe present invention, two or more kinds of polymers (B) that aredifferent in weight-average molecular weight from each other may be usedin the form of a mixture thereof.

The melt viscosity (as measured at 38° C.) of the polymer (B) ispreferably from 0.1 to 3,000 Pa·s, more preferably from 0.6 to 2,800Pa·s, still more preferably from 1.5 to 2,600 Pa·s and most preferablyfrom 1.5 to 800 Pa·s. When the melt viscosity of the polymer (B) fallswithin the above-specified range, the resulting rubber composition canbe easily kneaded and can be improved in processability. Meanwhile, inthe present specification, the melt viscosity of the polymer (B) is thevalue measured by the method described below in Examples.

The molecular weight distribution (Mw/Mn) of the polymer (B) ispreferably from 1.0 to 8.0, more preferably from 1.0 to 5.0 and stillmore preferably from 1.0 to 3.0. When the molecular weight distribution(Mw/Mn) of the polymer (B) falls within the above-specified range, theresulting polymer (B) can suitably exhibit a less variation in viscositythereof.

The glass transition temperature of the polymer (B) may vary dependingupon a vinyl content or the other monomer content thereof, and ispreferably from −90 to 0° C. and more preferably from −90 to −10° C.When the glass transition temperature of the polymer (B) falls withinthe above-specified range, the resulting rubber composition can exhibita good rolling resistance performance. The vinyl content of the polymer(B) is preferably 99% by mass or less and more preferably 90% by mass orless.

In the present invention, the polymer (B) is preferably compounded in anamount of from 0.1 to 100 parts by mass, more preferably from 0.5 to 50parts by mass and still more preferably from 1 to 30 parts by mass onthe basis of 100 parts by mass of the rubber component (A). When theamount of the polymer (B) compounded falls within the above-specifiedrange, the resulting rubber composition can exhibit good processability,mechanical strength and rolling resistance performance.

Meanwhile, in the case where the carbon black (C) has an averageparticle size of 60 nm or less, the polymer (B) is preferably compoundedin an amount of from 0.1 to 100 parts by mass, more preferably from 0.5to 50 parts by mass and still more preferably from 1 to 30 parts by masson the basis of 100 parts by mass of the rubber component (A). When theamount of the polymer (B) compounded falls within the above-specifiedrange, the resulting rubber composition can exhibit more excellentprocessability, mechanical strength and rolling resistance performance.

The polymer (B) may be produced by an emulsion polymerization method,the methods described in WO 2010/027463A and WO 2010/027464A or thelike. Among these methods, preferred are an emulsion polymerizationmethod and a solution polymerization method, and more preferred is asolution polymerization method.

(Emulsion Polymerization Method)

The emulsion polymerization method for producing the polymer (B) may beany suitable conventionally known method. For example, predeterminedamount of a farnesene monomer is emulsified and dispersed in thepresence of an emulsifying agent, and then the resulting emulsion issubjected to emulsion polymerization using a radical polymerizationinitiator.

As the emulsifying agent, there may be used, for example, a long-chainfatty acid salt having 10 or more carbon atoms or a rosinic acid salt.Specific examples of the emulsifying agent include potassium salts andsodium salts of fatty acids such as capric acid, lauric acid, myristicacid, palmitic acid, oleic acid and stearic acid.

As the dispersant for the emulsion polymerization, there may be usuallyused water, and the dispersant may also contain a water-soluble organicsolvent such as methanol and ethanol unless the use of such an organicsolvent gives any adverse influence on stability of the polymerization.

Examples of the radical polymerization initiator include persulfatessuch as ammonium persulfate and potassium persulfate; and organicperoxides and hydrogen peroxide.

In order to adjust a molecular weight of the resulting polymer (B),there may be used a chain transfer agent. Examples of the chain transferagent include mercaptans such as t-dodecyl mercaptan and n-dodecylmercaptan; and carbon tetrachloride, thioglycolic acid, diterpene,terpinolene, γ-terpinene and an α-methyl styrene dimer.

The temperature used upon the emulsion polymerization may beappropriately determined according to the kind of radical polymerizationinitiator used therein, and is usually preferably from 0 to 100° C. andmore preferably from 0 to 60° C. The polymerization method may be eithera continuous polymerization method or a batch polymerization method. Thepolymerization reaction may be stopped by adding a terminating agent tothe reaction system.

Examples of the terminating agent include amine compounds such asisopropyl hydroxylamine, diethyl hydroxylamine and hydroxylamine;quinone-based compounds such as hydroquinone and benzoquinone; andsodium nitrite.

After stopping the polymerization reaction, an antioxidant may be added,if required. Further, after stopping the polymerization reaction,unreacted monomers may be removed from the resulting latex, if required.Thereafter, the resulting polymer (B) is coagulated by adding a saltsuch as sodium chloride, calcium chloride and potassium chloride as acoagulant thereto and, if required, while adjusting a pH value of thecoagulation system by adding an acid such as nitric acid and sulfuricacid thereto, and then the dispersing solvent is separated from thereaction solution to recover the polymer (B). The thus recovered polymeris washed with water and dehydrated, and then dried to obtain thepolymer (B). Meanwhile, upon coagulating the polymer, the latex may bepreviously mixed, if required, with an extender oil in the form of anemulsified dispersion to recover the polymer (B) in the form of anoil-extended rubber.

(Solution Polymerization Method)

The solution polymerization method for producing the polymer (B) may beany suitable conventionally known method. For example, a farnesenemonomer may be polymerized in a solvent using a Ziegler-based catalyst,a metallocene-based catalyst or an anion-polymerizable active metal, ifrequired, in the presence of a polar compound.

Examples of the solvent used in the solution polymerization includealiphatic hydrocarbons such as n-butane, n-pentane, isopentane,n-hexane, n-heptane and isooctane; alicyclic hydrocarbons such ascyclopentane, cyclohexane and methyl cyclopentane; and aromatichydrocarbons such as benzene, toluene and xylene.

Examples of the anion-polymerizable active metal include alkali metalssuch as lithium, sodium and potassium; alkali earth metals such asberyllium, magnesium, calcium, strontium and barium; andlanthanoid-based rare earth metals such as lanthanum and neodymium.Among these active metals, preferred are alkali metals and alkali earthmetals, and more preferred are alkali metals. The alkali metals are morepreferably used in the form of an organic alkali metal compound.

Specific examples of the organic alkali metal compound include organicmonolithium compounds such as methyl lithium, ethyl lithium, n-butyllithium, sec-butyl lithium, t-butyl lithium, hexyl lithium, phenyllithium and stilbene lithium; polyfunctional organic lithium compoundssuch as dilithiomethane, dilithionaphthalene, 1,4-dilithiobutane,1,4-dilithio-2-ethyl cyclohexane and 1,3,5-trilithiobenzene; and sodiumnaphthalene and potassium naphthalene. Among these organic alkali metalcompounds, preferred are organic lithium compounds, and more preferredare organic monolithium compounds. The amount of the organic alkalimetal compound used may be appropriately determined according to amolecular weight of the farnesene polymer as required, and is preferablyfrom 0.01 to 3 parts by mass on the basis of 100 parts by mass offarnesene.

The organic alkali metal compound may be used in the form of an organicalkali metal amide by allowing a secondary amine such as dibutyl amine,dihexyl amine and dibenzyl amine to react therewith.

The polar compound may be used in the anion polymerization forcontrolling a microstructure of farnesene moieties without causingdeactivation of the reaction. Examples of the polar compound includeether compounds such as dibutyl ether, tetrahydrofuran and ethyleneglycol diethyl ether; tertiary amines such as tetramethylethylenediamine and trimethylamine; and alkali metal alkoxides andphosphine compounds. The polar compound is preferably used in an amountof from 0.01 to 1,000 mol equivalent on the basis of the organic alkalimetal compound.

The temperature used in the above polymerization reaction is usuallyfrom −80 to 150° C., preferably from 0 to 100° C. and more preferablyfrom 10 to 90° C. The polymerization method may be either a batch methodor a continuous method.

The polymerization reaction may be stopped by adding a terminating agentsuch as methanol and isopropanol to the reaction system. The resultingpolymerization reaction solution may be poured into a poor solvent suchas methanol to precipitate the polymer (B). Alternatively, thepolymerization reaction solution may be washed with water, and then asolid is separated therefrom and dried to isolate the polymer (B)therefrom.

{Modified Polymer}

The thus obtained polymer (B) may be subjected to modificationtreatment. Examples of a functional group used in the modificationtreatment include an amino group, an amide group, an imino group, animidazole group, a urea group, an alkoxysilyl group, a hydroxyl group,an epoxy group, an ether group, a carboxyl group, a carbonyl group, amercapto group, an isocyanate group, a nitrile group and an acidanhydride group.

As the method of producing the modified polymer, there may be used, forexample, the method in which before adding the terminating agent, acoupling agent such as tin tetrachloride, dibutyl tin chloride,tetrachlorosilane, dimethyl dichlorosilane, dimethyl diethoxysilane,tetramethoxysilane, tetraethoxysilane, 3-aminopropyl triethoxysilane,tetraglycidyl-1,3-bisaminomethyl cyclohexane and 2,4-tolylenediisocyanate which are capable of reacting with an active end of thepolymer chain, a chain end-modifying agent such as4,4′-bis(diethylamino)benzophenone, N-vinyl pyrrolidone,N-methylpyrrolidone, 4-dimethylaminobenzylidene aniline and dimethylimidazolidinone, or the other modifying agent as described in JP2011-132298A is added to the polymerization reaction system. Further,the isolated polymer may be grafted with maleic anhydride or the like.

In the modified polymer, the site of the polymer into which thefunctional group is introduced may be either a chain end or a side chainof the polymer. In addition, these functional groups may be used incombination of any two or more thereof. The modifying agent may be usedin an amount of from 0.1 to 10 mol equivalent on the basis of theorganic alkali metal compound.

<Carbon Black (C)>

The carbon black (C) used in the rubber composition of the presentinvention has an average particle size of from 5 to 100 nm. When theaverage particle size of the carbon black (C) is less than 5 nm, thecarbon black tends to exhibit a deteriorated dispersibility in therubber composition. When the average particle size of the carbon black(C) is more than 100 nm, the resulting rubber composition may fail toexhibit sufficient mechanical strength and hardness.

Examples of the carbon black (C) usable in the present invention includecarbon blacks such as furnace black, channel black, thermal black,acetylene black and Ketjen black. Among these carbon blacks, from theviewpoints of a high curing rate and an improved mechanical strength ofthe rubber composition, preferred is furnace black.

Examples of commercially available furnace black as the carbon black (C)having an average particle size of from 5 to 500 nm include “DIABLACK”available from Mitsubishi Chemical Corp., and “SEAST” available fromTokai Carbon Co., Ltd. Examples of commercially available acetyleneblack as the carbon black (C) having an average particle size of from 5to 500 nm include “DENKABLACK” available from Denki Kagaku Kogyo K.K.Examples of commercially available Ketjen black as the carbon black (C)having an average particle size of from 5 to 500 nm include “ECP600JD”available from Lion Corp.

The carbon black (C) may be subjected to an acid treatment with nitricacid, sulfuric acid, hydrochloric acid or a mixed acid thereof or may besubjected to a heat treatment in the presence of air for a surfaceoxidation treatment thereof, from the viewpoint of improving awettability or a dispersibility of the carbon black (C) in the rubbercomponent (A) and the polymer (B). In addition, from the viewpoint ofimproving a mechanical strength of the rubber composition of the presentinvention, the carbon black may be subjected to a heat treatment at atemperature of from 2,000 to 3,000° C. in the presence of agraphitization catalyst. As the graphitization catalyst, there may besuitably used boron, boron oxides (such as, for example, B₂O₂, B₂O₃,B₄O₃ and B₄O₅), oxo acids of boron (such as, for example, orthoboricacid, metaboric acid and tetraboric acid) and salts thereof, boroncarbonates (such as, for example, B₄C and B₆C), boron nitride (such asBN) and other boron compounds.

The average particle size of the carbon black (C) may be controlled bypulverization or the like. In order to pulverize the carbon black (C),there may be used a high-speed rotary mill (such as a hammer mill, a pinmil and a cage mill) or various ball mills (such as a rolling mill, avibration mill and a planetary mill), a stirring mill (such as a beadsmill, an attritor, a flow tube mill and an annular mill) or the like.

Meanwhile, the average particle size of the carbon black (C) may bedetermined by calculating an average value of diameters of carbon blackparticles measured using a transmission electron microscope.

In the rubber composition of the present invention, the carbon black (C)is compounded in an amount of from 20 to 100 parts by mass on the basisof 100 parts by mass of the rubber component (A). When the amount of thecarbon black (C) compounded is more than 100 parts by mass, theresulting rubber composition tends to be deteriorated in processability,dispersibility of the carbon black (C) therein and rolling resistanceperformance. On the other hand, when the amount of the carbon black (C)compounded is less than 20 parts by mass, the resulting rubbercomposition tends to be deteriorated in mechanical strength andhardness. The amount of the carbon black (C) compounded in the rubbercomposition on the basis of 100 parts by mass of the rubber component(A) is preferably 30 parts by mass or more, more preferably 40 parts bymass or more, still more preferably 43 parts by mass or more, andfurther still more preferably 45 parts by mass or more, and also ispreferably 95 parts by mass or less, more preferably 90 parts by mass orless, still more preferably 85 parts by mass or less, and further stillmore preferably 80 parts by mass or less.

More specifically, the amount of the carbon black (C) compounded in therubber composition on the basis of 100 parts by mass of the rubbercomponent (A) is preferably from 30 to 100 parts by mass, morepreferably from 40 to 90 parts by mass and still more preferably from 45to 80 parts by mass.

<Optional Components>

In the present invention, for the purposes of enhancing a mechanicalstrength of the rubber composition, improving various properties such asa heat resistance and a weathering resistance thereof, controlling ahardness thereof, and further improving economy by adding an extenderthereto, the rubber composition may also contain a filler other than thecarbon black (C), if required.

The filler other than the carbon black (C) may be appropriately selectedaccording to the applications of the obtained rubber composition. Forexample, as the filler, there may be used one or more fillers selectedfrom the group consisting of organic fillers, and inorganic fillers suchas silica, clay, talc, mica, calcium carbonate, magnesium hydroxide,aluminum hydroxide, barium sulfate, titanium oxide, glass fibers,fibrous fillers and glass balloons. Among these fillers, preferred issilica. Specific examples of the silica include dry silica (anhydroussilicic acid) and wet silica (anhydrous silicic acid). Among thesesilicas, from the viewpoint of enhancing a mechanical strength of theresulting rubber composition, preferred is wet silica. The above filleris preferably compounded in the rubber composition of the presentinvention in an amount of from 0.1 to 120 parts by mass, more preferablyfrom 5 to 90 parts by mass and still more preferably from 10 to 80 partsby mass on the basis of 100 parts by mass of the rubber component (A).When the amount of the filler compounded falls within theabove-specified range, the resulting rubber composition can befurthermore improved in mechanical strength.

Meanwhile, when compounding silica as an optional component, it ispreferred that the silica be added together with a silane couplingagent. Examples of the silane coupling agent includebis(3-triethoxysilylpropyl)tetrasulfide,bis(3-triethoxysilylethyl)tetrasulfide,bis(3-trimethoxysilylpropyl)tetrasulfide,bis(3-triethoxysilylpropyl)trisulfide andbis(3-triethoxysilylpropyl)disulfide. Among these silane couplingagents, bis(3-triethoxysilylpropyl)tetrasulfide is preferred because ofan excellent processability of the resulting rubber composition. Thesesilane coupling agents may be used alone or in combination of any two ormore thereof. The silane coupling agent is preferably compounded in therubber composition in an amount of from 0.1 to 15 parts by mass on thebasis of 100 parts by mass of the rubber component (A).

The rubber composition of the present invention may also contain, ifrequired, a softening agent for the purpose of improving aprocessability, a flowability or the like of the resulting rubbercomposition unless the effects of the present invention are adverselyinfluenced. Examples of the softening agent include a process oil suchas a silicone oil, an aroma oil, TDAE (treated distilled aromaticextracts), MES (mild extracted solvates), RAE (residual aromaticextracts), a paraffin oil and a naphthene oil; and a liquid polymer suchas a low-molecular weight polybutadiene, a low-molecular weightpolyisoprene, a low-molecular weight styrene-butadiene copolymer and alow-molecular weight styrene-isoprene copolymer. Meanwhile, the abovecopolymers may be in the form of either a block copolymer or a randomcopolymer. The liquid polymer preferably has a weight-average molecularweight of from 2,000 to 80,000 from the viewpoint of a goodprocessability of the resulting rubber composition. The above processoil or liquid polymer as a softening agent is preferably compounded inthe rubber composition of the present invention in an amount of lessthan 50 parts by mass on the basis of 100 parts by mass of the rubbercomponent (A).

The rubber composition of the present invention may also contain, ifrequired, one or more additives selected from the group consisting of anantioxidant, an oxidation inhibitor, a lubricant, a light stabilizer, ascorch retarder, a processing aid, a colorant such as pigments andcoloring matters, a flame retardant, an antistatic agent, a delusteringagent, an anti-blocking agent, an ultraviolet absorber, a release agent,a foaming agent, an antimicrobial agent, a mildew-proofing agent and aperfume, for the purposes of improving a weathering resistance, a heatresistance, an oxidation resistance or the like of the resulting rubbercomposition, unless the effects of the present invention are adverselyinfluenced.

Examples of the oxidation inhibitor include hindered phenol-basedcompounds, phosphorus-based compounds, lactone-based compounds andhydroxyl-based compounds.

Examples of the antioxidant include amine-ketone-based compounds,imidazole-based compounds, amine-based compounds, phenol-basedcompounds, sulfur-based compounds and phosphorus-based compounds.

The rubber composition of the present invention is preferably used inthe from of a crosslinked product produced by adding a crosslinkingagent thereto.

Examples of the crosslinking agent include sulfur and sulfur compounds,oxygen, organic peroxides, phenol resins and amino resins, quinone andquinone dioxime derivatives, halogen compounds, aldehyde compounds,alcohol compounds, epoxy compounds, metal halides and organic metalhalides, and silane compounds. Among these crosslinking agents,preferred are sulfur and sulfur compounds. These crosslinking agents maybe used alone or in combination of any two or more thereof. Thecrosslinking agent is preferably compounded in the rubber composition inan amount of from 0.1 to 10 parts by mass on the basis of 100 parts bymass of the rubber component (A).

When using sulfur as the crosslinking agent, a vulcanization aid or avulcanization accelerator is preferably used in combination with thecrosslinking agent.

Examples of the vulcanization aid include fatty acids such as stearicacid and metal oxides such as zinc oxide.

Examples of the vulcanization accelerator include guanidine-basedcompounds, sulfene amide-based compounds, thiazole-based compounds,thiuram-based compounds, thiourea-based compounds, dithiocarbamicacid-based compounds, aldehyde-amine-based compounds,aldehyde-ammonia-based compounds, imidazoline-based compounds andxanthate-based compounds. These vulcanization aids or vulcanizationaccelerators may be used alone or in combination of any two or morethereof. The vulcanization aid or vulcanization accelerator ispreferably compounded in the rubber composition of the present inventionin an amount of from 0.1 to 15 parts by mass on the basis of 100 partsby mass of the rubber component (A).

The method for producing the rubber composition of the present inventionis not particularly limited, and any suitable method may be used in thepresent invention as long as the respective components are uniformlymixed with each other.

The method of uniformly mixing the respective components may be carriedout using a closed type kneader of a tangential type or a meshing typesuch a kneader rudder, a Brabender, a Banbury mixer and an internalmixer, a single-screw extruder, a twin-screw extruder, a mixing roll, aroller or the like in a temperature range of usually from 70 to 270° C.

[Tire]

The tire of the present invention is produced by using the rubbercomposition of the present invention at least in a part thereof, andtherefore can exhibit a good mechanical strength and an excellentrolling resistance performance.

EXAMPLES

The present invention will be described in more detail below byreferring to the following examples. It should be noted, however, thatthe following examples are only illustrative and not intended to limitthe invention thereto.

Examples 1 to 23 and Comparative Examples 1 to 15

The weight-average molecular weight, melt viscosity, vinyl content andglass transition temperature of the polymer (B), the Mooney viscosity ofthe rubber composition, the dispersibility of the carbon black (C) inthe rubber composition, and the rolling resistance performance, hardnessand tensile strength at break of the rubber composition, were measuredby the following methods.

(1) Weight-Average Molecular Weight

The weight-average molecular weight (Mw) and the molecular weightdistribution (Mw/Mn) of the polymer (B) were measured by GPC (gelpermeation chromatography) in terms of a molecular weight of polystyreneas a reference standard substance. The measuring apparatuses andconditions are as follows.

-   -   Apparatus: GPC device “GPC8020” available from Tosoh Corp.    -   Separating column: “TSKgelG4000HXL” available from Tosoh Corp.    -   Detector: “RI-8020” available from Tosoh Corp.    -   Eluent: Tetrahydrofuran    -   Eluent flow rate: 1.0 mL/min    -   Sample concentration: 5 mg/10 mL    -   Column temperature: 40° C.        (2) Melt Viscosity

The melt viscosity of the polymer (B) was measured at 38° C. using aBrookfield viscometer available from Brookfield Engineering Labs. Inc.

(3) Vinyl Content

A solution prepared by dissolving 50 mg of the polymer (B) in 1 mL ofCDCl₃ was subjected to ¹H-NMR measurement at 400 MHz at a cumulativefrequency of 512 times. From the chart obtained by the abovemeasurement, a spectrum portion in the range of from 4.94 to 5.22 ppmwas regarded as being a spectrum derived from a vinyl structure, whereasa spectrum portion in the range of from 4.45 to 4.85 ppm was regarded asbeing a combined spectrum derived from both the vinyl structure and a1,4-bond, and the vinyl content of the polymer (B) was calculatedaccording to the following formula.{Vinyl Content}=(integrated value from 4.94 to 5.22 ppm)/2/{(integratedvalue from 4.94 to 5.22 ppm)/2+[(integrated value from 4.45 to 4.85ppm)−(integrated value from 4.94 to 5.22 ppm)]/3}(4) Glass Transition Temperature

Ten milligrams of the polymer (B) were sampled in an aluminum pan, and athermogram of the sample was measured at temperature rise rate of 10°C./min by differential scanning calorimetry (DSC), and the value at apeak top observed in the DDSC curve was determined as a glass transitiontemperature of the polymer (B).

(5) Mooney Viscosity

As an index of a processability of the rubber composition, the Mooneyviscosity (ML1+4) of the rubber composition before being cured wasmeasured at 100° C. according to JIS K6300. The values of the respectiveExamples and Comparative Examples appearing in Table 2 are relativevalues based on 100 as the value of Comparative Example 3. Also, thevalues of the respective Examples and Comparative Examples appearing inTables 3 and 4 are relative values based on 100 as the value ofComparative Example 8; and the values of the respective Examples andComparative Examples appearing in Group 1, Group 2, Group 3, Group 4 andGroup 5 in Table 5 are relative values based on 100 as each of thevalues of Comparative Example 11, Comparative Example 12, ComparativeExample 13, Comparative Example 14 and Comparative Example 15,respectively. Meanwhile, the smaller Mooney viscosity value indicates amore excellent processability.

(6) Dispersibility of Carbon Black

The rubber composition was press-molded to prepare a cured sheet(thickness: 2 mm). The thus prepared sheet was cut into a test piecehaving a section of 2 mm×6 mm, and the section was observed using anoptical microscope and visually evaluated by counting the number ofaggregated carbon black masses having a size of 20 μm or more on thesection. The evaluation ratings are as follows:

[1]: There were present 1 to 7 coagulated carbon black masses.

[2]: There were present 8 to 14 coagulated carbon black masses.

[3]: There were present 15 to 21 coagulated carbon black masses.

[4]: There were present 22 or more coagulated carbon black masses.

Meanwhile, the smaller value indicates a more excellent dispersibilityof the carbon black in the rubber composition.

(7) Rolling Resistance Performance

The rubber composition was press-molded to prepare a cured sheet(thickness; 2 mm). The thus prepared sheet was cut into a test piecehaving a size of 40 mm in length×7 mm in width. The thus obtained testpiece was subjected to measurement of tan δ as an index of a rollingresistance performance of the rubber composition using a dynamicviscoelasticity measuring apparatus available from GABO GmbH under theconditions including a measuring temperature of 60° C., a frequency of10 Hz, a static distortion of 10% and a dynamic distortion of 2%. Thevalues of the respective Examples and Comparative Examples appearing inTable 2 are relative values based on 100 as the value of ComparativeExample 3. Also, the values of the respective Examples and ComparativeExamples appearing in Tables 3 and 4 are relative values based on 100 asthe value of Comparative Example 8; and the values of the respectiveExamples and Comparative Examples appearing in Group 1, Group 2, Group3, Group 4 and Group 5 in Table 5 are relative values based on 100 aseach of the values of Comparative Example 11, Comparative Example 12,Comparative Example 13, Comparative Example 14 and Comparative Example15, respectively. Meanwhile, the smaller value indicates a excellentrolling resistance performance of the rubber composition.

(8) Hardness

According to JIS K6253, the rubber composition was press-molded toprepare a cured sheet (thickness: 2 mm). The hardness of the thusprepared sheet was measured using a type-A hardness tester, and the thusmeasured hardness was used as an index of a flexibility of the rubbercomposition. Meanwhile, when the hardness value is less than 50, a tireproduced from the rubber composition suffers from large deformation andtherefore is deteriorated in steering stability.

(9) Tensile Strength at Break

The rubber composition was press-molded to prepare a cured sheet(thickness: 2 mm). The thus prepared sheet was punched into adumbbell-shaped test piece according to JIS 3, and the obtained testpiece was subjected to measurement of a tensile strength at breakthereof using a tensile tester available from Instron Corp. The valuesof the respective Examples and Comparative Examples appearing in Table 2are relative values based on 100 as the value of Comparative Example 3.Also, the values of the respective Examples and Comparative Examplesappearing in Tables 3 and 4 are relative values based on 100 as thevalue of Comparative Example 8; and the values of the respectiveExamples and Comparative Examples appearing in Group 1, Group 2, Group3, Group 4 and Group 5 in Table 5 are relative values based on 100 aseach of the values of Comparative Example 11, Comparative Example 12,Comparative Example 13, Comparative Example 14 and Comparative Example15, respectively. Meanwhile, the larger value indicates a higher tensilestrength at break of the rubber composition.

Production Example 1 Production of Polyfarnesene (B-1)

A pressure reaction vessel previously purged with nitrogen and thendried was charged with 120 g of hexane as a solvent and 1.1 g of n-butyllithium (in the form of a 17% by mass hexane solution) as an initiator.The contents of the reaction vessel were heated to 50° C., and 210 g ofPlarnesene were added thereto and polymerized for 1 h. The resultingpolymerization reaction solution was treated with methanol and thenwashed with water. After separating water from the thus washedpolymerization reaction solution, the resulting solution was dried at70° C. for 12 h, thereby obtaining a polyfarnesene (B-1). Variousproperties of the thus obtained polyfarnesene (B-1) are shown in Table1.

Production Example 2 Production of Polyfarnesene (B-2)

A pressure reaction vessel previously purged with nitrogen and thendried was charged with 203 g of hexane as a solvent and 7.7 g of n-butyllithium (in the form of a 17% by mass hexane solution) as an initiator.The contents of the reaction vessel were heated to 50° C., and 342 g ofβ-farnesene were added thereto and polymerized for 1 h. The resultingpolymerization reaction solution was treated with methanol and thenwashed with water. After separating water from the thus washedpolymerization reaction solution, the resulting solution was dried at70° C. for 12 h, thereby obtaining a polyfarnesene (B-2). Variousproperties of the thus obtained polyfarnesene (B-2) are shown in Table1.

Production Example 3 Production of Polyfarnesene (B-3)

A pressure reaction vessel previously purged with nitrogen and thendried was charged with 274 g of hexane as a solvent and 1.2 g of n-butyllithium (in the form of a 17% by mass hexane solution) as an initiator.The contents of the reaction vessel were heated to 50° C., and 272 g ofβ-farnesene were added thereto and polymerized for 1 h. The resultingpolymerization reaction solution was treated with methanol and thenwashed with water. After separating water from the thus washedpolymerization reaction solution, the resulting solution was dried at70° C. for 12 h, thereby obtaining a polyfarnesene (B-3). Variousproperties of the thus obtained polyfarnesene (B-3) are shown in Table1.

Production Example 4 Production of Polyfarnesene (B-4)

A pressure reaction vessel previously purged with nitrogen and thendried was charged with 313 g of hexane as a solvent and 0.7 g of n-butyllithium (in the form of a 17% by mass hexane solution) as an initiator.The contents of the reaction vessel were heated to 50° C., and 226 g ofβ-farnesene were added thereto and polymerized for 1 h. The resultingpolymerization reaction solution was treated with methanol and thenwashed with water. After separating water from the thus washedpolymerization reaction solution, the resulting solution was dried at70° C. for 12 h, thereby obtaining a polyfarnesene (B-4). Variousproperties of the thus obtained polyfarnesene (B-4) are shown in Table1.

Production Example 5 Production of Polyisoprene

The same procedure as in Production Example 1 was repeated except forusing isoprene in place of β-farnesene, thereby obtaining apolyisoprene. Various properties of the thus obtained polyisoprene areshown in Table 1.

Production Example 6 Production of Polyfarnesene (B-6)

A pressure reaction vessel previously purged with nitrogen and thendried was charged with 240 g of cyclohexane as a solvent and 1.7 g ofn-butyl lithium (in the form of a 17% by mass hexane solution) as aninitiator. The contents of the reaction vessel were heated to 50° C.,and 0.5 g of N,N,N′,N′-tetramethyl ethylenediamine and further 340 g ofβ-farnesene were added thereto and polymerized for 1 h. The resultingpolymerization reaction solution was treated with methanol and thenwashed with water. After separating water from the thus washedpolymerization reaction solution, the resulting solution was dried at70° C. for 12 h, thereby obtaining a polyfarnesene (B-6). Variousproperties of the thus obtained polyfarnesene (B-6) are shown in Table1.

Production Example 7 Production of Polyfarnesene (B-7)

A pressure reaction vessel was charged with 500 g of polyfarneseneproduced by the same method as described in Production Example 3, 0.5 gof “NOCRAC 6C” as an antioxidant, and 2.5 g of maleic anhydride. Afterpurging the reaction vessel with nitrogen, the contents of the reactionvessel were heated to 170° C. and reacted at that temperature for 10 h,thereby obtaining a polyfarnesene (B-7). Various properties of the thusobtained polyfarnesene (B-7) are shown in Table 1.

Production Example 8 Production of Polyfarnesene (B-8)

A pressure reaction vessel previously purged with nitrogen and thendried was charged with 241 g of cyclohexane as a solvent and 28.3 g ofsec-butyl lithium (in the form of a 10.5% by mass cyclohexane solution)as an initiator. The contents of the reaction vessel were heated to 50°C., and then 342 g of β-farnesene were added thereto and polymerized for1 h. The resulting polymerization reaction solution was treated withmethanol and then washed with water. After separating water from thethus washed polymerization reaction solution, the resulting solution wasdried at 70° C. for 12 h, thereby obtaining a polyfarnesene (B-8).Various properties of the thus obtained polyfarnesene (B-8) are shown inTable 1.

TABLE 1 Molecular Weight-average weight Glass transition moleculardistribution Vinyl content temperature Melt viscosity Polymer weight(×10³) Mw/Mn (mass %) (° C.) (at 38° C.) (Pa · s) ProductionPolyfarnesene 90 1.2 7 −73 24 Example 1 (B-1) Production Polyfarnesene30 1.2 8 −73 4 Example 2 (B-2) Production Polyfarnesene 140 1.2 7 −73 69Example 3 (B-3) Production Polyfarnesene 430 1.5 7 −73 2200 Example 4(B-4) Production Polyisoprene 60 1.1 − − 480 Example 5 ProductionPolyfarnesene 100 1.1 50  −66 62 Example 6 (B-6) ProductionPolyfarnesene 140 1.2 7 −71 90 Example 7 (B-7) Production Polyfarnesene10 1.1 8 −73 0.9 Example 8 (B-8)

The respective components including the natural rubber (A), the polymer(B), the carbon black (C) or the like used in the following Examples andComparative Examples are as follows.

Natural Rubber:

SMR20 (natural rubber from Malaysia)

STR20 (natural rubber from Thailand)

Styrene-Butadiene Rubber:

“JSR1500” available from JSR Corp.; weight-average molecular weight:450,000; styrene content: 23.5% by weight (produced by emulsionpolymerization method)

Butadiene Rubber:

“BR-01” available from JSR Corp.

Polymer (B):

Polyfarnesenes (B-1) to (B-4) and (B-6) to (B-8) produced above inProduction Examples 1 to 4 and 6 to 8

Carbon Black (C):

C-1: “DIABLACK H” available from Mitsubishi Chemical Corp.; averageparticle size: 30 nm

C-2: “DIABLACK E” available from Mitsubishi Chemical Corp.; averageparticle size: 50 nm

C-3: “SEAST TA” available from Tokai Carbon Co., Ltd.; average particlesize: 120 nm

C-4: “DIABLACK I” available from Mitsubishi Chemical Corp.; averageparticle size: 20 nm

C-5: “SEAST V” available from Tokai Carbon Co., Ltd.; average particlesize: 60 nm

Optional Components

Polyisoprene: Polyisoprene produced in Production Example 5

TDAE: “VivaTec500” available from H & R Corp.

Resin: “ESCOREZ 1102” available from Exxon Mobil Corp.

Stearic Acid: “LUNAC S-20” available from Kao Corp.

Zinc Oxide: Zinc oxide available from Sakai Chemical Industry Co., Ltd.

Antioxidant (1): “NOCRAC 6C” available from Ouchi Shinko ChemicalIndustrial Co., Ltd.

Antioxidant (2): “ANTAGE RD” available from Kawaguchi Chemical IndustryCo., Ltd.

Wax: “SUNTIGHT S” available from Seiko Chemical Co., Ltd.

Sulfur: Sulfur fine powder 200 mesh available from Tsurumi ChemicalIndustry Co., Ltd.

Vulcanization accelerator: “NOCCELER NS” available from Ouchi ShinkoChemical Industrial Co., Ltd.

The rubber component (A), polymer (B), carbon black (C), stearic acid,zinc oxide and antioxidant(s) were charged at such a compounding ratio(part(s) by mass) as shown in Tables 2 to 5 into a closed type Banburymixer and kneaded together for 6 min such that the initiatingtemperature was 75° C. and the resin temperature reached 160° C. Theresulting mixture was once taken out of the mixer, and cooled to roomtemperature. Next, the mixture was placed in a mixing roll, and afteradding sulfur and the vulcanization accelerator thereto, the contents ofthe mixing roll were kneaded at 60° C. for 6 min, thereby obtaining arubber composition. The Mooney viscosity of the thus obtained rubbercomposition was measured by the above method.

In addition, the resulting rubber composition was press-molded (at 145°C. for 20 min) while being cured to prepare a sheet (thickness: 2 mm).The thus prepared sheet was evaluated for a dispersibility of carbonblack therein, a rolling resistance performance, a hardness and atensile strength at break by the above methods. The results are shown inTables 2 to 5.

TABLE 2 Comparative Examples Examples 1 2 3 4 5 1 2 3 Compounding ratio(part(s) by mass) Component (A) Natural rubber (SMR20) 100 100 100 100100 100 100 100 Styrene-butadiene rubber Butadiene rubber Component (B)Polyfarnesene (B-1) 10 10 10 Polyfarnesene (B-2) 10 Polyfarnesene (B-3)10 Polyfarnesene (B-4) 10 Polyfarnesene (B-6) Maleic-modifiedpolyfarnesene (B-7) Polyfarnesene (B-8) TDAE Resin: “ESCOREZ 1102”Polyisoprene 10 Component (C) Carbon black (C-1) 50 50 50 50 50 50Carbon black (C-2) 50 Carbon black (C-3) 50 Carbon black (C-4) Carbonblack (C-5) Optional Components Stearic acid 2 2 2 2 2 2 2 2 Zinc oxide3.5 3.5 3.5 3.5 3.5 3.5 3.5 3.5 Antioxidant (1) 1 1 1 1 1 1 1 1Antioxidant (2) Wax Sulfur 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 Vulcanizationaccelerator 1 1 1 1 1 1 1 1 Properties Mooney viscosity (relative value)76 75 76 84 63 56 80 100 Dispersibility of carbon black 1 1 2 2 1 1 3 3Rolling resistance performance (at 60° C.; tanδ) 69 82 69 81 60 55 95100 (relative value) Hardness (type A) 58 56 59 61 56 48 60 64 Tensilestrength at break (relative value) 92 95 92 94 82 79 100 100

The rubber compositions obtained in Examples 1 to 5 were prevented frombeing deteriorated in mechanical strength and hardness, and enhanced indispersibility of carbon black therein. In addition, the rubbercompositions obtained in Examples 1 to 3 exhibited a low Mooneyviscosity and a good processability. Further, the rubber compositionsobtained in Examples 1 and 3 exhibited especially a low rollingresistance and therefore could be suitably used as a rubber compositionfor tires.

TABLE 3 Examples Comparative Examples 6 7 8 9 10 11 12 13 14 4 5 6 7 8Compounding ratio (part(s) by mass) Component (A) Natural rubber (STR20)100 100 100 100 100 100 100 100 100 100 100 100 100 100Styrene-butadiene rubber Butadiene rubber Component (B) Polyfarnesene(B-1) Polyfarnesene (B-2) Polyfarnesene (B-3) 1 3 5 7 10 20 10 10Polyfarnesene (B-4) Polyfarnesene (B-6) 10 Maleic 10 anhydride-modifiedpolyfarnesene (B-7) Polyfarnesene (B-8) TDAE Resin: “ESCOREZ 1102”Polyisoprene 1 5 10 Component (C) Carbon black (C-1) 50 50 50 50 50 5050 50 30 15 50 50 50 50 Carbon black (C-2) Carbon black (C-3) Carbonblack (C-4) Carbon black (C-5) Optional Components Stearic acid 2 2 2 22 2 2 2 2 2 2 2 2 2 Zinc oxide 3.5 3.5 3.5 3.5 3.5 3.5 3.5 3.5 3.5 3.53.5 3.5 3.5 3.5 Antioxidant (1) 1 1 1 1 1 1 1 1 1 1 1 1 1 1 Antioxidant(2) Wax Sulfur 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5Vulcanization 1 1 1 1 1 1 1 1 1 1 1 1 1 1 accelerator Properties Mooneyviscosity (relative 74 80 97 93 88 85 77 57 58 40 100 92 81 100 value)Dispersibility of carbon 1 1 2 1 1 1 1 1 1 1 3 3 3 3 black Rollingresistance 89 97 101 99 94 87 80 95 53 34 104 105 109 100 performance(at 60° C.; tanδ) (relative value) Hardness (type A) 60 61 64 65 63 6359 53 50 41 65 63 59 66 Tensile strength at break 92 90 99 95 96 92 9184 99 93 98 98 93 100 (relative value)

TABLE 4 Comparative Examples Examples 15 16 9 10 Compounding ratio(part(s) by mass) Component (A) Natural rubber (STR20) 100 100 100 100Styrene-butadiene rubber Butadiene rubber Component (B) Polyfarnesene(B-1) Polyfarnesene (B-2) Polyfarnesene (B-3) 30 50 Polyfarnesene (B-4)Polyfarnesene (B-6) Maleic acid-modified polyfarnesene (B-7)Polyfarnesene (B-8) TDAE 30 50 Resin: “ESCOREZ 1102” PolyisopreneComponent (C) Carbon black (C-1) 80 80 80 80 Carbon black (C-2) Carbonblack (C-3) Carbon black (C-4) Carbon black (C-5) Optional ComponentsStearic acid 2 2 2 2 Zinc oxide 3.5 3.5 3.5 3.5 Antioxidant (1) 1 1 1 1Antioxidant (2) Wax Sulfur 1.5 1.5 1.5 1.5 Vulcanization accelerator 1 11 1 Properties Mooney viscosity (relative value) 71 47 75 49Dispersibility of carbon black 2 2 4 4 Rolling resistance performance119 130 128 140 (at 60° C.; tanδ) (relative value) Hardness (type A) 6355 62 56 Tensile strength at break (relative value) 67 52 — —

TABLE 5 Group 1 Group 2 Group 3 Group 4 Group 5 Com. Com. Com. Com. Com.Ex. 17 Ex. 11 Ex. 18 Ex. 12 Ex. 19 Ex. 13 Ex. 20 Ex. 14 Ex. 21 Ex. 22Ex. 23 Ex. 15 Compounding ratio (part(s) by mass) Component (A) Naturalrubber 100 100 100 100 50 50 80 80 100 100 100 100 (STR20)Styrene-butadiene 20 20 rubber Butadiene rubber 50 50 Component (B)Polyfarnesene (B-1) Polyfarnesene (B-2) Polyfarnesene (B-3) 2 3 3 5 7 77 Polyfarnesene (B-4) Polyfarnesene (B-6) Maleic anhydride- modifiedpolyfarnesene (B-7) Polyfarnesene (B-8) 3 TDAE 3 3 Resin: 2 “ESCOREZ1102” Polyisoprene 3 5 3 10 Component (C) Carbon black (C-1) 45 45 50 5050 50 50 50 Carbon black (C-2) Carbon black (C-3) Carbon black (C-4) 5050 Carbon black (C-5) 55 55 Optional Components Stearic acid 2 2 2 2 2 22 2 2 2 2 2 Zinc oxide 3.5 3.5 3.5 3.5 3.5 3.5 3.5 3.5 3.5 3.5 3.5 3.5Antioxidant (1) 1 1 1 1 3 3 1 1 1 1 1 1 Antioxidant (2) 0.5 0.5 1 1 0.50.5 Wax 2 2 Sulfur 1.6 1.6 1.5 1.5 1.2 1.2 1.5 1.5 1.5 1.5 1.5 1.5Vulcanization 2 2 1.2 1.2 0.75 0.75 1 1 1 1 1 1 accelerator PropertiesMooney viscosity 99 100 100 100 97 100 99 100 99 93 92 100 (relativevalue) Dispersibility of 2 3 1 2 1 3 1 3 1 1 1 3 carbon black Rollingresistance 83 100 90 100 98 100 92 100 82 83 85 100 performance (at 60°C.; tanδ) (relative value) Hardness (type A) 71 70 60 60 55 56 61 62 6060 59 59 Tensile strength at 99 100 102 100 103 100 100 100 99 100 99100 break (relative value)

As shown in Table 3, the rubber compositions obtained in Examples 6 to14 exhibited a good processability owing to a low Mooney viscositythereof, were enhanced in dispersibility of carbon black therein, andwere prevented from being deteriorated in hardness. In addition, theserubber compositions had a low rolling resistance and therefore could besuitably used as a rubber composition for tires.

Among them, from the comparison between Examples 6 and 7, andComparative Example 7, it was confirmed that the effects of the presentinvention could be exhibited irrespective of a vinyl content andmodification or non-modification of the rubber compositions.

From the comparison between Example 8 and Comparative Example 5, betweenExample 10 and Comparative Example 6 and between Example 12 andComparative Example 7, it was confirmed that when using the polymer (B),the resulting rubber compositions were excellent in all ofprocessability, dispersibility of carbon black and rolling resistanceperformance.

In addition, from the comparison between Example 14 and ComparativeExample 4, it was confirmed that when adjusting the content of thecarbon black (C) to 20 parts by mass or more based on 100 parts by massof the rubber component (A), the resulting rubber composition wasprevented from being deteriorated in hardness and could be suitably usedas a composition for tires.

As shown in Table 4, from the comparison between Example 15 andComparative Example 9 and between Example 16 and Comparative Example 10,it was confirmed that when adjusting the content of the carbon black (C)to 100 parts by mass or less based on 100 parts by mass of the rubbercomponent (A), the resulting rubber compositions were excellent in allof processability, dispersibility of carbon black and rolling resistanceperformance.

As shown in Table 5, from the comparison between Example 17 andComparative Example 11 and between Example 18 and Comparative Example12, it was confirmed that when using the carbon black (C) having anaverage particle size of from 5 to 100 nm, the resulting rubbercompositions exhibited a good processability and were prevented frombeing deteriorated in hardness and therefore could provide a rubbercomposition for tires having an excellent rolling resistanceperformance.

In addition, from the comparison between Example 19 and ComparativeExample 13 and between Example 20 and Comparative Example 14, it wasconfirmed that even when using a mixture containing two or more kinds ofnatural and synthetic rubbers as the rubber component (A), it waspossible to attain the effects of the present invention.

Further, from the comparison between Examples 21 to 23 and ComparativeExample 15, it was confirmed that even when using two or more kinds ofpolymers (B) or using the polymer (B) in combination with the otheroptional components, it was also possible to attain the effects of thepresent invention.

Examples 24 to 28 and Comparative Examples 16 to 19

The respective components including the natural rubber (A), the polymer(B), the carbon black (C) or the like used in Examples 24 to 28 andComparative Examples 16 to 19 are as follows.

Rubber Component (A);

Styrene-butadiene rubber “JSR1500” available from JSR Corp.;weight-average molecular weight: 450,000; styrene content: 23.5% byweight (produced by emulsion polymerization method)

Polymer (B):

Polyfarnesenes (B-9) to (B-12) produced in Production Examples 9 to 12

Carbon Black (C):

C-1: “DIABLACK H” available from Mitsubishi Chemical Corp.; averageparticle size: 30 nm

C-2: “DIABLACK E” available from Mitsubishi Chemical Corp.; averageparticle size; 50 nm

C-3: “SEAST TA” available from Tokai Carbon Co., Ltd.; average particlesize: 120 nm

Optional Components

Polyisoprene: Polyisoprene produced in Production Example 13

TDAE: “VivaTec500” available from H & R Corp.

Stearic Acid: “LUNAC S-20” available from Kao Corp.

Zinc Oxide: Zinc oxide available from Sakai Chemical Industry Co., Ltd.

Antioxidant (1): “NOCRAC 6C” available from Ouchi Shinko ChemicalIndustrial Co., Ltd.

Antioxidant (2): “ANTAGE RD” available from Kawaguchi Chemical IndustryCo., Ltd.

Sulfur: Sulfur fine powder 200 mesh available from Tsurumi ChemicalIndustry Co., Ltd.

Vulcanization accelerator (1): “NOCCELER CZ-G” available from OuchiShinko Chemical Industrial Co., Ltd.

Vulcanization accelerator (2): “NOCCELER D” available from Ouchi ShinkoChemical Industrial Co., Ltd.

Production Example 9 Production of Polyfarnesene (B-9)

A pressure reaction vessel previously purged with nitrogen and thendried was charged with 120 g of hexane and 1.1 g of n-butyl lithium (inthe form of a 17% by mass hexane solution). The contents of the reactionvessel were heated to 50° C., and 210 g of β-farnesene were addedthereto and polymerized for 1 h. The resulting polymerization reactionsolution was mixed with methanol and then washed with water. Afterseparating water from the thus washed polymerization reaction solution,the resulting solution was dried at 70° C. for 12 h, thereby obtaining apolyfarnesene (B-9) having properties shown in Table 6.

Production Example 10 Production of Polyfarnesene (B-10)

A pressure reaction vessel previously purged with nitrogen and thendried was charged with 241 g of cyclohexane and 28.3 g of sec-butyllithium (in the form of a 10.5% by mass cyclohexane solution). Thecontents of the reaction vessel were heated to 50° C., and 342 g ofβ-farnesene were added thereto and polymerized for 1 h. The resultingpolymerization reaction solution was mixed with methanol and then washedwith water. After separating water from the thus washed polymerizationreaction solution, the resulting solution was dried at 70° C. for 12 h,thereby obtaining a polyfarnesene (B-10) having properties shown inTable 6.

Production Example 11 Production of Polyfarnesene (B-11)

A pressure reaction vessel previously purged with nitrogen and thendried was charged with 274 g of hexane and 1.2 g of n-butyl lithium (inthe form of a 17% by mass hexane solution). The contents of the reactionvessel were heated to 50° C., and 272 g of Plarnesene were added theretoand polymerized for 1 h. The resulting polymerization reaction solutionwas mixed with methanol and then washed with water. After separatingwater from the thus washed polymerization reaction solution, theresulting solution was dried at 70° C. for 12 h, thereby obtaining apolyfarnesene (B-11) having properties shown in Table 6.

Production Example 12 Production of Polyfarnesene (B-12)

A pressure reaction vessel previously purged with nitrogen and thendried was charged with 313 g of hexane and 0.7 g of n-butyl lithium (inthe form of a 17% by mass cyclohexane solution). The contents of thereaction vessel were heated to 50° C., and 226 g of β-farnesene wereadded thereto and polymerized for 1 h. The resulting polymerizationreaction solution was mixed with methanol and then washed with water.After separating water from the thus washed polymerization reactionsolution, the resulting solution was dried at 70° C. for 12 h, therebyobtaining a polyfarnesene (B-12) having properties shown in Table 6.

Production Example 13 Production of Polyisoprene

A pressure reaction vessel previously purged with nitrogen and thendried was charged with 600 g of hexane and 44.9 g of n-butyl lithium (inthe form of a 17% by mass hexane solution). The contents of the reactionvessel were heated to 70° C., and then 2050 g of isoprene were addedthereto and polymerized for 1 h. The resulting polymerization reactionsolution was mixed with methanol and then washed with water. Afterseparating water from the thus washed polymerization reaction solution,the resulting solution was dried at 70° C. for 12 h, thereby obtainingpolyisoprene having properties shown in Table 6.

The weight-average molecular weight and melt viscosity of each of thepolymer (B) and polyisoprene were measured by the following methods.

(Method of Measuring Weight-Average Molecular Weight)

The weight-average molecular weight (Mw) and the molecular weightdistribution (Mw/Mn) of each of the polymer (B) and polyisoprene weremeasured by GPC (gel permeation chromatography) in terms of a molecularweight of polystyrene as a reference standard substance. The measuringapparatuses and conditions are as follows.

-   -   Apparatus: GPC device “GPC8020” available from Tosoh Corp.    -   Separating column: “TSKgelG4000HXL” available from Tosoh Corp.    -   Detector: “RI-8020” available from Tosoh Corp.    -   Eluent: Tetrahydrofuran    -   Eluent flow rate: 1.0 mL/min    -   Sample concentration: 5 mg/10 mL    -   Column temperature: 40° C.        (Method of Measuring Melt Viscosity)

The melt viscosity of the polymer (B) was measured at 38° C. using aBrookfield viscometer available from Brookfield Engineering Labs. Inc.

TABLE 6 Molecular Melt Weight-average weight viscosity moleculardistribution (at 38° C.) Polymer weight (×10³) Mw/Mn (Pa · s) ProductionPolyfarnesene 90 1.2 24 Example 9 (B-9) Production Polyfarnesene 10 1.10.9 Example 10 (B-10) Production Polyfarnesene 140 1.2 69 Example 11(B-11) Production Polyfarnesene 430 1.5 2200 Example 12 (B-12)Production Polyisoprene 32 1.1 74 Example 13

The rubber component (A), polymer (B), polyisoprene, carbon black (C),TDAE, stearic acid, zinc oxide and antioxidants were charged at such acompounding ratio (part(s) by mass) as shown in Table 7 into a closedtype Banbury mixer and kneaded together for 6 min such that theinitiating temperature was 75° C. and the resin temperature reached 160°C. The resulting mixture was once taken out of the mixer, and cooled toroom temperature. Next, the mixture was placed in a mixing roll, andafter adding sulfur and the vulcanization accelerators thereto, thecontents of the mixing roll were kneaded at 60° C. for 6 min, therebyobtaining a rubber composition. The Mooney viscosity of the thusobtained rubber composition was measured by the below-mentioned method.

In addition, the resulting rubber composition was press-molded (at 145°C. for 20 min) to prepare a sheet (thickness: 2 mm). The thus preparedsheet was evaluated for a dispersibility of carbon black therein, arolling resistance performance, a hardness, a tensile elongation atbreak and a tensile strength at break by the below-mentioned methods.The results are shown in Table 7.

Meanwhile, the methods of evaluating the Mooney viscosity of the rubbercomposition and the dispersibility of the carbon black in the rubbercomposition, and the methods of measuring the rolling resistanceperformance, hardness, tensile elongation at break and tensile strengthat break of the rubber composition, are as follows.

(1) Mooney Viscosity

As an index of a processability of the rubber composition, the Mooneyviscosity (ML1+4) of the rubber composition before being cured wasmeasured at 100° C. according to JIS K6300. The values of the respectiveExamples and Comparative Examples appearing in Table 7 are relativevalues based on 100 as the value of Comparative Example 19. Meanwhile,the smaller Mooney viscosity value indicates a more excellentprocessability.

(2) Dispersibility of Carbon Black

The sheet obtained from the rubber composition produced in therespective Examples and Comparative Examples was cut into a test piecehaving a section of 2 mm×6 mm, and the section was observed using anoptical microscope and visually evaluated by counting the number ofcoagulated carbon black masses having a size of 20 μm or more on thesection. The evaluation ratings are as follows:

[1]: There were present 1 to 3 coagulated carbon black masses.

[2]: There were present 4 to 6 coagulated carbon black masses.

[3]: There were present 7 to 9 coagulated carbon black masses.

[4]: There were present 10 or more coagulated carbon black masses.

The smaller value indicates a more excellent dispersibility of carbonblack in the rubber composition.

(3) Rolling Resistance Performance

The sheet obtained from the rubber composition produced in therespective Examples and Comparative Examples was cut into a test piecehaving a size of 40 mm in length×7 mm in width. The thus obtained testpiece was subjected to measurement of tan δ as an index of a rollingresistance performance of the rubber composition using a dynamicviscoelasticity measuring apparatus available from GABO GmbH under theconditions including a measuring temperature of 60° C., a frequency of10 Hz, a static distortion of 10% and a dynamic distortion of 2%. Thevalues of the respective Examples and Comparative Examples are relativevalues based on 100 as the value of Comparative Example 19. Meanwhile,the smaller value indicates a higher rolling resistance performance ofthe rubber composition.

(4) Hardness

According to JIS K6253, the hardness of the sheet obtained from therubber composition produced in the respective Examples and ComparativeExamples was measured using a type-A hardness tester, and the thusmeasured hardness was used as an index of a flexibility of the rubbercomposition. Meanwhile, when the hardness value is less than 50, a tireproduced from the rubber composition suffers from large deformation andtherefore is deteriorated in steering stability.

(5) Tensile Elongation at Break

The sheet obtained from the rubber composition produced in therespective Examples and Comparative Examples was punched into adumbbell-shaped test piece according to JIS 3, and the obtained testpiece was subjected to measurement of a tensile elongation at breakthereof using a tensile tester available from Instron Corp. The valuesof the respective Examples and Comparative Examples are relative valuesbased on 100 as the value of Comparative Example 19. Meanwhile, thelarger value indicates a higher tensile elongation at break of therubber composition.

(6) Tensile Strength at Break

The sheet obtained from the rubber composition produced in therespective Examples and Comparative Examples was punched into adumbbell-shaped test piece according to JIS 3, and the obtained testpiece was subjected to measurement of a tensile strength at breakthereof using a tensile tester available from Instron Corp. The valuesof the respective Examples and Comparative Examples are relative valuesbased on 100 as the value of Comparative Example 19. Meanwhile, thelarger value indicates a higher tensile strength at break of the rubbercomposition.

TABLE 7 Examples Comparative Examples 24 25 26 27 28 16 17 18 19Compounding ratio (part(s) by mass) Component (A) Styrene-butadienerubber 100 100 100 100 100 100 100 100 100 Component (B) Polyfarnesene(B-9) 10 10 10 Polyfarnesene (B-10) 10 Polyfarnesene (B-11) 10Polyfarnesene (B-12) 10 Component (C) Carbon black (C-1) 50 50 50 50 5050 50 Carbon black (C-2) 50 Carbon black (C-3) 50 Optional ComponentsPolyisoprene 10 TDAE 10 Stearic acid 1 1 1 1 1 1 1 1 1 Zinc oxide 3.53.5 3.5 3.5 3.5 3.5 3.5 3.5 3.5 Antioxidant (1) 1 1 1 1 1 1 1 1 1Antioxidant (2) 1 1 1 1 1 1 1 1 1 Sulfur 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.51.5 Vulcanization accelerator (1) 1 1 1 1 1 1 1 1 1 Vulcanizationaccelerator (2) 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 Properties Mooneyviscosity (relative value) 67 63 67 74 55 67 50 70 100 Dispersibility ofcarbon black 1 2 2 2 1 3 2 4 3 Rolling resistance performance (at 60°C.; tanδ) 98 107 98 100 85 104 80 111 100 (relative value) Hardness(type A) 59 56 59 61 55 59 48 60 66 Tensile elongation at break(relative value) 117 138 115 115 110 121 115 127 100 Tensile strength atbreak (relative value) 91 97 92 93 80 93 75 94 100

The rubber compositions obtained in Examples 24 to 28 exhibited a lowMooney viscosity and a good processability. In addition, the rubbercompositions obtained in Examples 24. 26 and 28 were enhanced indispersibility of carbon black therein, and exhibited a low rollingresistance. In particular, the rubber compositions obtained in Examples24 and 26 were prevented from being deteriorated in mechanical strengthand hardness, and therefore could be suitably used as a rubbercomposition for tires.

The invention claimed is:
 1. A rubber composition comprising: (A) atleast one rubber component selected from the group consisting of asynthetic rubber and a natural rubber; (B) a polymer of farnesene havinga weight-average molecular weight of from 25,000 to 500,000 and a meltviscosity of from 0.1 to 3,000 Pa·s as measured at 38° C.; and (C)carbon black having an average particle size of from 5 to 100 nm,wherein a content of the polymer (B) in the rubber composition is from0.1 to 100 parts by mass on the basis of 100 parts by mass of the rubbercomponent (A), and wherein a content of the carbon black (C) in therubber composition is from 20 to 100 parts by mass on the basis of 100parts by mass of the rubber component (A).
 2. The rubber compositionaccording to claim 1, wherein the polymer (B) is a homopolymer ofβ-farnesene.
 3. The rubber composition according to claim 1, wherein theat least one synthetic rubber is present and is at least one selectedfrom the group consisting of a styrene-butadiene rubber, a butadienerubber and an isoprene rubber.
 4. The rubber composition according toclaim 3, wherein the at least one synthetic rubber comprises thestyrene-butadiene rubber and the styrene-butadiene rubber has aweight-average molecular weight of from 100,000 to 2,500,000.
 5. Therubber composition according to claim 3, wherein the at least onesynthetic rubber comprises the styrene-butadiene rubber and thestyrene-butadiene rubber has a styrene content of from 0.1 to 70% bymass, based on the total mass of the styrene-butadiene rubber.
 6. Therubber composition according to claim 3, wherein the at least onesynthetic rubber comprises the butadiene rubber and the butadiene rubberhas a weight-average molecular weight of from 90,000 to 2,000,000. 7.The rubber composition according to claim 3, wherein the at least onesynthetic rubber comprises the butadiene rubber and the butadiene rubberhas a vinyl content of 50% by mass or less, based on the total mass ofthe butadiene rubber.
 8. The rubber composition according to claim 1,wherein the polymer (B) has a molecular weight distribution, Mw/Mn, offrom 1.0 to 8.0, wherein Mw is the weight-average molecular weight andMn is the number-average molecular weight.
 9. A tire at least partiallycomprising the rubber composition according to claim 1.